Dialkyl(2-methylimidazolyl)metal tetramers of Group III elements: crystal and molecular structure of tetrakis-µ-(2-methylimidazolyl)tetrakis(diethylgallium)

Abstract

A series of compounds [R₂ML]₄(R = Me, M = B, Al, Ga, and In; R = Et, M = Ga; L = 2-methylimidazolyl) has been synthesized by reaction of Group III metal trialkyls with molar equivalents of 2-methylimidazole. The products have been characterized and the X-ray crystal structure of the Et₂Ga derivative determined. Crystals are monoclinic, a= 15.31(2), b= 19.39(3), c= 14.21(2)Å, β= 101.30(9)°, space group I2/a, Z= 4 (tetrameric units). The structure was determined from diffractometer data by Patterson and Fourier methods, and refined by full-matrix least-squares methods to R 0.101 for 1 182 observed reflexions. The molecule consists of four diethyl-gallium moieties linked by 2-methylimidazolyl rings to form a ‘square’ of side 6 Å. The molecule has pseudo-D_2d symmetry and crystallographic two-fold symmetry, the two-fold axis passing through two of the gallium atoms. Mean dimensions are: Ga–N 1.98, Ga–C 1.90, N–C 1.36, C–CH₃ 1.46 Å; N–Ga–N 102, C–Ga–C 124, and N–Ga–C 107°.